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Modeling of wind flow around tree for CFD simulation
Ryuichi Inoue, Kyoto University
Kazuyoshi Nishijima, DPRI, Kyoto University (Speaker)
UNESCO-JASTIP Joint Symposium on Intra-Regional Water Securityand Disaster Management, Quezon City, the Philippines, November 16, 2017
Bangladesh, courtesy of Prof. Ando
17/04/2008
西嶋一欽 京都大学防災研究所 2会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 2UNESCO-JASTIP Symposium Modelling of wind field around tree
• Field surveys on vernacular constructions in southeast Asia.
• Damage survey after typhoon Yolanda with UP Diliman in 2014, J-RAPID project.
• Damage survey after hurricane Pam in Vanuatu in 2015
Observations
• Damages on non-engineered construction with industrial materials.
• Sometimes, traditional constructions behave wellunder extreme events.
Background
Samar, the Philippines
Bangladesh
Tanna, Vanuatu
17/04/2008
西嶋一欽 京都大学防災研究所 3会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 3UNESCO-JASTIP Symposium Modelling of wind field around tree
Motivation
• Re-evaluate the performance of traditional construction techniques by state-of-the-art technology engineering tools.
• Justify the advantages of the traditional techniques, where true.
Engineeringknowledge body
Pro
gre
ss
Engineeringfrontier
Non-engineeredsystems
Feed
back
JSPS project: 16H05905, Grant-in-Aid for Young Scientists (A), Re-evaluation of vernacular
disaster mitigation technologies by engineering manner – case of wind-induced disaster
(2016-2019)
17/04/2008
西嶋一欽 京都大学防災研究所 4会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 4UNESCO-JASTIP Symposium Modelling of wind field around tree
Some ongoing projects in our research team
• JASTIP WP4 in corporation with the University of the Philippines, Diliman, 2015-2020.
Telecommunication tower
New tower
Incoming wind
Boundary layer
AnemometersAnemometer
More anemometers
Wind
Kapit Bahay 1.0developed by UPD
Physical computing
• JICA grass-root project“Advancement of vernacular constructions in Tanna island, the Republic of Vanuatu”, 2016-2018.
Full-scale testingIntelligent anemometer
17/04/2008
西嶋一欽 京都大学防災研究所 5会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 5UNESCO-JASTIP Symposium Modelling of wind field around tree
Today’s talk is...Wind-breaking effect of tree
Contents
• Objective of research
• Wind tunnel experiment
• CFD simulation
• Optimized aerodynamic parameters in CFD
17/04/2008
西嶋一欽 京都大学防災研究所 6会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 6UNESCO-JASTIP Symposium Modelling of wind field around tree
Objective
Challenge addressed in this research
• Current canopy models do not consider mechanical characteristics of tree behavior under various wind speed; hence, fail to simulate wind field accurately.
Goal of the research
• To develop a canopy model that can simulate wind flow affected by tree and other plants.
Wind tunnel (2m/s)
Wind tunnel (4m/s)
17/04/2008
西嶋一欽 京都大学防災研究所 7会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 7UNESCO-JASTIP Symposium Modelling of wind field around tree
Wind tunnel experiment
17/04/2008
西嶋一欽 京都大学防災研究所 8会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 8UNESCO-JASTIP Symposium Modelling of wind field around tree
Tree model
• Tree model consists of trunk, branches and leaves.
• Made of timber, acryl and plastic film respectively.
• Leaves are connected to branches with silicon tubes.
• Leaves are painted white for image analysis.
330m
m120m
m
20°Φ5mmacryl tube
Φ24mmTimber solid pole
Leaf area density: 4.7
Leaf area density: 4.8
Leaf area density: 4.65
500mmplastic film
Top view Side view
(m2/m3)
17/04/2008
西嶋一欽 京都大学防災研究所 9会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 9UNESCO-JASTIP Symposium Modelling of wind field around tree
330
120
(Unit: mm)
Inflow wind condition
• Uniform flow
• Wind speed: 2, 4 and 8 m/s
U: Mean wind speed
Ur: Reference wind speed (at 510mm)
σu: Standard deviation of wind speed
z: height
Average time = 30 sec.
17/04/2008
西嶋一欽 京都大学防災研究所 10会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 10UNESCO-JASTIP Symposium Modelling of wind field around tree
Measurement condition
Measurements
• Wind speed measured with I-shape hotwire probe.
• Drag force acting on the tree model with aerodynamic balance.
• Motion of the tree model with video camera.
120
(mm)
wind
600 400
600 400
30m
m×
14
420
30m
m×
24
Measurement pointSide view
Top viewFloor
z
xo
x
o
y
1000
500
Pitottube
1000
500wind
17/04/2008
西嶋一欽 京都大学防災研究所 11会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 11UNESCO-JASTIP Symposium Modelling of wind field around tree
Result: horizontal wind profile behind tree model
• Wind speed reductionbehind the tree model
• Wind speed recoveryin furtherer points.
Horizontal wind speed profile at height of 300 mm at x=600 mm and 1000mm.
wind 540
z
xo
500
1000-1000
U0(z)U(z)
Pitot
600
(mm)
17/04/2008
西嶋一欽 京都大学防災研究所 12会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 12UNESCO-JASTIP Symposium Modelling of wind field around tree
Result: Drag force
• (Projected) leaf area density, a
• Drag coefficient, Cf
2 2
1 2A B
D u d u d Drag force:
ρ:Air density
u:Wind speed
σ:Area
Theory A B
Object
Du1 u2
A’ B’
Measured drag force Calculated Cf a
17/04/2008
西嶋一欽 京都大学防災研究所 13会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 13UNESCO-JASTIP Symposium Modelling of wind field around tree
Result: Aerodynamic parameters
• (Projected) leaf area density, a
• Drag coefficient, Cf
2 2
1 2A B
D u d u d Drag force:
ρ:Air density
u:Wind speed
σ:Area
Theory A B
Object
Du1 u2
A’ B’
Observations
• Aerodynamic parameters depend on wind speed
• Drag force (hence, aerodynamic parameters) are interrelated to the change of the wind speed profile
“Optimal” aerodynamic parameters are identified by CFD simulation.
Measured drag force Calculated Cf a
17/04/2008
西嶋一欽 京都大学防災研究所 14会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 14UNESCO-JASTIP Symposium Modelling of wind field around tree
CFD simulation
17/04/2008
西嶋一欽 京都大学防災研究所 15会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 15UNESCO-JASTIP Symposium Modelling of wind field around tree
Generation of inflow
• Boundary condition
–Ceil boundary: slip
–Side boundary: slip
–Floor boundary: canopy model
• Grid condition
–X direction:20mm
–Y direction:10mm
–Z direction:10mm - 80mm
–Volume:18m×2.5m×2.01m
xy
z
O
2.0
1m
2.5m
Analysis of wind flow around the tree model
Generation of inflow
17/04/2008
西嶋一欽 京都大学防災研究所 16会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 16UNESCO-JASTIP Symposium Modelling of wind field around tree
Generated inflow
*u is calculated based on 0.01-sec averaged wind speed.
17/04/2008
西嶋一欽 京都大学防災研究所 17会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 17UNESCO-JASTIP Symposium Modelling of wind field around tree
xy
z
O
Analysis condition around the tree model
• Boundary condition
–Ceil boundary: slip
–Side boundary: slip
–Floor boundary: canopy model
• Grid condition
–X direction:20mm
–Y direction:20mm
–Z direction:20mm - 60mm
–Volume:3.5m×2.5m×2.01m
17/04/2008
西嶋一欽 京都大学防災研究所 18会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 18UNESCO-JASTIP Symposium Modelling of wind field around tree
Re-parameterization of aerodynamic parameters
• (Projected) leaf area density, a
• Drag coefficient, Cf
x-direction wind speedat z=280mm
''
f f
aaC a C
a
Wind speed dependent
Re-parameterization
Wind speed dependent
Leaf area density under no wind
17/04/2008
西嶋一欽 京都大学防災研究所 19会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 19UNESCO-JASTIP Symposium Modelling of wind field around tree
Result: simplistic modelling of tree
wind
330
Three layered cuboids
330
Rotated three layered cuboids
wind
More precise modeling required.
17/04/2008
西嶋一欽 京都大学防災研究所 20会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 20UNESCO-JASTIP Symposium Modelling of wind field around tree
Detailed tree modeling for CFD
• Image of tree silhouette at wind speed=0m/s
• Binary analysis (black: no object, : object)
– If an
17/04/2008
西嶋一欽 京都大学防災研究所 21会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 21UNESCO-JASTIP Symposium Modelling of wind field around tree
Optimized aerodynamic parameters
Comparison of CFD results and experiment results at x=600, z=300
Optimized aerodynamic parametersa’: Projected leaf area density
under no wind
a: Projected leaf area density
Cf: Drag parameter
Adjusted drag parameter
2 4 8a' 19.8 19.8 19.8
a /a'*C f 0.4 0.3 0.2
Wind speed(m/s)
17/04/2008
西嶋一欽 京都大学防災研究所 22会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 22UNESCO-JASTIP Symposium Modelling of wind field around tree
Conclusion
• A tree model for wind tunnel experiment is developed
– It can show the wind-speed dependence characteristics of aerodynamic parameters.
• Simplistic modeling approach for tree in terms of canopy model fails to reproduce the wind speed profile behind the tree in CFD.
• An elaborated modeling approach shows a potential to be able to reproduce the wind speed profile.
• We will have a tool to evaluate the advantages of wind-breaking forest on wind-resistant performance of buildings.
17/04/2008
西嶋一欽 京都大学防災研究所 23会議名 発表タイトル17/04/2008
Kazuyoshi Nishijima, DPRI-KU 23UNESCO-JASTIP Symposium Modelling of wind field around tree
“to measure is to know –
if you cannot measure it,
you cannot improve it”
Lord Kelvin
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